feat: Add JWT authentication to all API calls in settings and dashboard

- Fixed settings.tsx: Added Clerk auth tokens to connection-status, disconnect-linkedin, disconnect-github, and save-settings API calls
- Fixed dashboard.tsx: Added auth tokens to 7 API calls (loadScheduledPosts, checkAuthentication, loadUsage, loadUserSettings, loadPostHistory, loadStats, savePost)
- Updated .env.example with missing variables (CLERK_ISSUER, DEV_MODE, DATABASE_URL, ENCRYPTION_KEY, ADMIN_EMAIL)
- Fixed bare except clauses with debug logging in post_history.py and ai_service.py
- Removed deprecated dashboard-old.tsx
- Added errorHandler.ts utility for consistent frontend error handling
- Security: DEV_MODE bypass now requires explicit DEV_MODE=true

Author: cliff-de-tech

.env.example

@@ -76,6 +76,32 @@ UNSPLASH_ACCESS_KEY=your_unsplash_access_key_here
 # 4. Copy the Signing Secret below
 CLERK_WEBHOOK_SECRET=whsec_your_signing_secret_here
 
+# Clerk issuer URL for JWT verification (REQUIRED for production)
+# Format: https://your-clerk-instance.clerk.accounts.dev
+CLERK_ISSUER=https://your-clerk-instance.clerk.accounts.dev
+
+# Development mode (set to 'true' only for local development)
+# WARNING: Never set to 'true' in production!
+DEV_MODE=false
+
+# ========================================
+# DATABASE (Production)
+# ========================================
+# PostgreSQL connection string for production
+# Format: postgresql://user:password@host:5432/database
+# Leave unset for local SQLite fallback
+# DATABASE_URL=postgresql://user:password@host:5432/database
+
+# ========================================
+# SECURITY - Token Encryption
+# ========================================
+# 32-byte key for encrypting OAuth tokens at rest
+# Generate with: python -c "import secrets; print(secrets.token_hex(32))"
+ENCRYPTION_KEY=your_64_char_hex_key_here
+
+# Admin email for receiving feedback notifications
+ADMIN_EMAIL=[email protected]
+
 # ========================================
 # DATABASE PATHS (Optional)
 # ========================================